Computers using memory such as dynamic random access memory (DRAM) are well known in the art. Personal computers such as IBM AT and compatibles, use such DRAM memories for a variety of functions. Development in the personal computer (PC) industry has been the widespread acceptance of single inline memory modules (SIMMS). Such SIMMS are used to lower the cost of memory and many higher density memory subsystems can be designed using SIMMS. Since the SIMMS are relatively small modules, they are used extensively in the computer industry to allow for the proper operation. The DRAM chips themselves are very reliable.
Therefore, errors due to the DRAM chip are less common than when PCs were first introduced. At the same time cost of the personal computers has dropped dramatically and profit margins have been squeezed by intense competition. Typically in known computer systems a particular type of SIMM module is utilized therewithin. That SIMM module requires a particular addressing scheme for adequate operation.
Hence, the addressing scheme is oftentimes limited to a particular type of DRAM, as there have become more and more different types of DRAMs. As more and different types of DRAMs come into existence with different types of addressing schemes, it becomes more difficult to design these different modules into a computer. This difficulty occurs because the memory controller used to control the SIMM module, or the memory within the computer, must generally be adaptable to driving one type of addressing scheme. To make a more complicated and complex memory controller would require additional expense to the personal computer. Many memories are not compatible with existing personal computers because their addressing schemes are very different than the existing addressing scheme.
More specifically, a typical computer system includes a memory controller addresses the SIMM module providing one half of the address bits during the row address strobe (RAS) and providing the other half of the address bits during the column address strobe (CAS) signal. These are some SIMM modules that can only be addressed asymmetrically, that is, there is an odd number of address bits required to efficiently access the memory. These types of SIMM modules cannot be utilized with a typical memory controller without substantial modification thereof. These modifications would require a redesigning of the memory controller to support the different SIMM modules. This may increase the engineering cost related to the computer system.
Accordingly, many SIMM module manufacturers cannot use these types of DRAMs because of their addressing scheme. What is desired therefore is a system for allowing for different types of memory modules with different addressing schemes to be substituted for existing memory modules, so as to allow for increased memory capacity with resultant lower cost associated with the new memory units. The system that is developed should be cost effective, should not add undue complexity to the existing circuitry, and should also be compatible with existing circuitry. The present invention addresses such a need.